The present invention relates to turbine blades for turbomachinery such as gas turbine engines and, more particularly, to improved geometrical shapes for such blades and the platform from which they extend.
Turbine blades are mounted circumferentially on an inner diameter platform about a turbine shaft to allow rotation thereof in streams of working medium fluids to extract energy and work therefrom as those fluids flow around and past such blades through the flow passages between them. Such flows can be transonic in accelerating from below the speed of sound coming into the blade region to being above the speed of sound in the exit region. In these situations inefficiencies due to shock wave losses are important.
Blade airfoil surface profiles and the geometry of the airfoil and the platform on which the blade is mounted become very important in achieving high efficiencies. In addition, a blade design to be suitable must minimize the penalties imposed on the engine system by the weight and cost of the blades, and need for cooling air therein, a goal sought through reducing the number of blades provided about the platform circumference for each blade stage used. However, the remaining blades must then extract more work, the lift or loading of the blade, from the fluid streams passing thereby which tends to reduce blade efficiency. A high lift blade will have a Zweifel lift coefficient (the ratio of the actual load to the ideal load) that is greater than 1.1. Thus, there is a desire for a blade that achieves high efficiency during transonic operation while having a large lift loading.